Functional evaluation of poly-(N-p-vinylbenzyl-O-beta-D-galactopyranosyl-[1-4]-D-gluconamide)(PVLA) as a liver specific carrier.

Hepatocytes express the specific C-type lectin, asialoglycoprotein (ASGP) receptor, on the surface to remove the ligand-bearing proteins from circulation. The specific expression and ligand specificity are thought to be the ideal characters for the target of drug or gene delivery. Various galactose-bearing molecules were synthesized for this purpose. However, the biological or functional interaction of these molecules with the ASGP receptor still remains to be elucidated. In this study. we evaluated the functional ability of synthetic galactose polymer ligand, poly-(N-p-vinylbenzyl-O-beta-D-galactopyranosyl-[1-4]-D-gluconamide) (PVLA), to interact with recombinant ASGP receptors using mouse ASGP receptor (mouse hepatic lectin; MHL) gene-transfected CHO cells. PVLA-coated beads bound to and were endocytosed by the whole (MHL-1/-2) ASGP receptor-expressing CHO cells like hepatocytes while PVMA (poly-(N-p-vinylbenzyl-O-beta-D-glucopyranosyl-[1-4]-D-gluconamide) did not. Interestingly, PVLA-coated beads were also endocytosed by either MHL-1 or MHL-2 alone expressing cells, which are known to be incapable of endocytosing natural ligands. In addition, the endocytosis of PVLA-coated beads by MHL-expressing CHO cells or primary hepatocytes was inhibited only by soluble PVLA but not by the same galactose molecular concentration of soluble asialofetuin. Furthermore, PVLA-coated beads were endocytosed by primary hepatocyte to a significantly higher degree than asialofetuin-coated beads in vitro. These results suggest that PVLA has higher affinity to the ASGP receptor than the natural ligands in blood. Consistently, it was demonstrated that intravenously injected FITC-labeled PVLA but not PVMA drastically accumulated in parenchymal cells of the liver in vivo. Taken together, PVLA exhibiting higher affinity with hepatocytes than natural ligands is thought to be an attractive and practical carrier-ligand for liver targeting.